6.1 Name TWO parts of a stator with reference to induction motors - NSC Electrical Technology Power Systems - Question 6 - 2023 - Paper 1

This nameplate indicates operational parameters such as voltage supply (400 V), current (5 A), and efficiency (85%), all of which are typical for three-phase motors. Additionally, the presence of three windings is implied by the parameters provided.

The efficiency of the motor, as indicated on the nameplate, is 85%. This means that 85% of the electrical power input is converted into mechanical power output.

To calculate the synchronous speed ( s) of the motor, use the formula:

s = rac{120 imes 50}{2} = 1500 ext{ r/min}$$

Slip (s) can be calculated using the formula: $s = n_s - n_{full ext{ load}}$ Substituting the values:

• $n_s$ = 1500 r/min (synchronous speed)
• $n_{full load}$ = 1250 r/min The calculation becomes: $s = 1500 - 1250 = 250 ext{ r/min}$

In a three-phase induction motor, power is transferred through electromagnetic induction. When the three-phase supply feeds current into the stator windings, it creates a rotating magnetic field. This field interacts with the rotor, inducing a current in it. As the rotor's magnetic field tries to align with the stator's rotating field, it creates torque that powers the rotor. This process converts electrical energy from the supply into mechanical energy in the rotor.

The torque-speed curve illustrates different operational points of the induction motor, indicating that as load increases, speed decreases until the breakdown point. Beyond this point, the motor will stall, showing the relationship between torque and speed, which is crucial for understanding motor performance under varying loads.